The main pulmonary artery (MPA) is intrapericardial and
courses posteriorly and superiorly from the pulmonic valve. It divides into the
left pulmonary artery (LPA) and right pulmonary artery (RPA) at the level of the
fifth thoracic vertebra. The RPA is longer than the LPA and crosses the
mediastinum, sloping slightly inferiorly to the right lung hilus. The LPA
represents the continuation of the MPA.

Segmental and subsegmental pulmonary arteries generally
parallel segmental and subsegmental bronchi and run alongside them. This is in
contrast to the course of most pulmonary veins, which run independently of
bronchi within interlobular septa. The segmental arteries are named according to
the bronchopulmonary segments that they feed, and we follow the Jackson and
Huber classification in this description. However, the proximal portions of the
arteries to the posterior subsegment of the left upper lobe and the lingular
arteries can run independently of their respective bronchi for short segments.
Also, there are frequently accessory arteries from neighboring segments,
particularly in the right upper lobe. Segmental and subsegmental pulmonary
arteries vary considerably in the location of their origins, in whether they
arise as common trunks with other arteries or as separate arteries, and in their
number.

This diagram may help simplify the segmental anatomy of the lung and the pulmonary arteries. It is only meant to simplify the anatomic relation of segments to one another within each lobe and not their exact anatomic locations.